A surface light source is not limited to merely illumination but is desired in many fields for decorations, advertisements, optical devices, etc.
As a prior art surface light source, electro-luminescence is in the spotlight, but, in actuality, it has not reached the point of practicality. A surface light source of this type is limited in its emitted light colors, and further its light quantity (or luminous energy) is not sufficient. Other than this, as a system for obtaining a surface light source, there is a system using light-guiding prisms, but with this system, a surface light-emitting source of small thickness cannot be obtained, and, moreover, there are problems with the light quantity and price.
At present, a common surface light source in practical use is a type wherein a plural number of fluorescent lamps are arranged in a row, and a diffusion plate is disposed in front thereof. However, with this system, in order to obtain a surface in which the light quantity has been equalized to an extent such that the forms of the fluorescent lamps cannot be distinguished, two or more diffusion plates must be used in superposition which greatly reduces the quantity if light transmitted from the light source. On one hand, with a surface light source of this type, since a light source, or sources, must always be disposed behind the light-emitting surface, the installation of the surface light source device is impossible in a case such as where there is no space for installation of the light source behind the light-emitting surface.
It is an object of this invention to provide a device for controlling light images which can be used as a surface light source device without the problems as described hereinbefore and, at the same time, also as a device for forming again or projecting a light image at a position remote therefrom and, further, can be used for various uses by causing light to pass through reverse paths.